Einatomige

Einatomige is an adjective used in physics and chemistry to describe matter that consists of single atoms rather than molecules composed of two or more atoms. In this sense, a material or species is monatomic if its stable form in the given conditions is an isolated atom. The term is often used interchangeably with monatomic in English and is commonly applied to noble gases, which exist as discrete atoms in the gas phase under standard conditions. It is contrasted with diatomic and polyatomic substances, such as O2, N2, H2, or H2O, which are bound as molecules.

Noble gases helium, neon, argon, krypton, xenon, and radon are the typical examples of monatomic gases. Some elements can exist as monatomic vapors in high-temperature or low-pressure environments; metals, under vaporization in thin films or vacuum deposition, can be present as monatomic atoms. Atomic hydrogen can also be monatomic in high-energy plasmas or dissociated gas streams.

In thermodynamics and kinetic theory, a monatomic ideal gas has three translational degrees of freedom and, in the simplest model, no rotational or vibrational contributions to the internal energy, leading to molar heat capacities Cv = 3/2 R and Cp = 5/2 R for ideal gases. Monatomic behavior is a baseline for comparing more complex molecular species, which possess additional rotational and vibrational modes.